The invention is concerned with a power-split transmission for motor vehicles with off-road travel, consisting of a case, of an input shaft, of a first output shaft coaxial with the latter, of a second output shaft offset with respect to said first output shaft, of a reduction unit, of a clutch unit and of an offset drive. This form of power-split transmission is also designated as “single-offset”. It is used, above all, for all-wheel driven passenger motor vehicles and light commercial vehicles with a longitudinally arranged engine/transmission block, while there can be a changeover from road travel to off-road travel by means of the reduction unit, an interaxle differential is often dispensed with and the drive of the second driven axle can be cut in.
A generic power-split transmission is known from EP 943 479 A1. In this, the reduction unit on the side of the input shaft is a planetary transmission with a ring gear fixed to the case and with power take-off at the planet carrier. Directly behind, the associated shift device is accommodated. This is followed, in one embodiment (FIG. 2), by a central differential and then the driving wheel of the offset drive; in another embodiment (FIG. 9), it is the driving wheel of the offset drive and, finally, a clutch for cutting in the second driven axle.
The reduction unit has various disadvantages. On account of the ring gear fixed to the case, the planetary transmission corotates with meshing even in road travel, thus increasing the losses, wear and generation of noise. Moreover, in the case of single-stage planetary transmissions of this form of construction, the design for achieving the reductions (2:1 to 3:1) customary for off-road travel results in unfavorably small planet wheels. The shift device between the planetary transmission and the driving wheel of the offset drive is not readily accessible, increases the construction length and displaces the offset drive to the rear, the latter factor being unfavorable, inter alia, for reasons of the radiation of solid-born sound through the case.
The object of the invention is, therefore, to eliminate the foregoing disadvantages. The power-split transmission is to be short and compact, with low loss and low noise and also suitable for modularization and the mounting of synchronization.